1. Field of the Invention
This invention relates to absorption filters employing absorbing dyes dispersed within a transparent binder. It is particularly adapted for laser eye protection.
2. Related Art
The demand for laser protective eyewear has rapidly increased in recent years. The traditional methodology is the use of color filter glass elements. Inorganic dopants which absorb or scatter near the wavelength of interest are mixed with the glass. For example, BG-18, KG-3 or KG-5 glass (manufactured by Schott Optical Company) are absorption filters that provide protection against lasers operating near the red end of the visible spectrum. Metal ions (such as nickel oxide, cobalt oxide or chromium oxide) or phosphate are the absorbing materials in these glasses. The dopants and silica glass are melted (typically at 1000.degree. C. to 1200.degree. C.), blended and cooled to resolidify. The filter is then formed from the bulk material. These glass filters have severe shortcomings however.
First, these filters do not provide protection from all of the wavelengths of current interest. Second, the glass provides no protection against ballistic fragments. Third, the absorption bandwidth is generally broader than desired. In the case of BG-18, the darkening material (cobalt oxide and chromium oxide) has very poor scotopic luminuous transmittance and severely limits transmittance in the red spectral region. Another general negative aspect of glass-based protective eyewear is its weight which contributes to long term wearer fatigue and discomfort.
A thin coating that could be applied to a light-weight, ballistic protective polycarbonate (PC), yet provide high optical density (OD) at a variety of selected wavelengths and high transmittance at other wavelengths, is therefore highly desirable and, heretofore, unknown.